The interesting question is how good are then at converting moving air into power - there is a clear upper limit based on the mass and velocity - a cubic metre of air is about 1kg, and if you have a 1m2 collector (and that fan is more like half that) then when the wind is at so many metres per second, then that many cubic metres ,each with a kinetic energy of 1/2 m.v² is the maximum that can be intercepted, and there fore the maximum available energy - but of course that would bring the air to a dead stop, which it cannot, so it is always a modest fraction of this upper bound. However it is a quick check which allows the wilder claims to be thrown out.

(more detail on that explanation here)

I'd expect the roof ridge ones to be more like a screw thread Darrius turbine on its side - if it isn't they have probably missed a trick.

Mike

The interesting question is how good are then at converting moving air into power - there is a clear upper limit based on the mass and velocity - a cubic metre of air is about 1kg, and if you have a 1m2 collector (and that fan is more like half that) then when the wind is at so many metres per second, then that many cubic metres ,each with a kinetic energy of 1/2 m.v² is the maximum that can be intercepted, and there fore the maximum available energy - but of course that would bring the air to a dead stop, which it cannot, so it is always a modest fraction of this upper bound. However it is a quick check which allows the wilder claims to be thrown out.

(more detail on that explanation here)

I'd expect the roof ridge ones to be more like a screw thread Darrius turbine on its side - if it isn't they have probably missed a trick.

Mike